Metal roof
Our energy consultants, Neo Virtus Engineering, evaluated our new home. The problem: it would get up to 90 degrees inside in the summer.
Their top priority recommendation was to install and metal roof. I understand about the need for high solar reflectance and thermal emissivity.
I’ve seen one home that has a standing seam design. Quite nice.
What metal (certainly not aluminum) would produce the highest SRI and TE? Should the panels be prepainted? Energy Star has many companies and colors to choose from.
I live in Ipswich and really would value your recommendations for a contractor.
Thank,
R.Addison
P.S.4/26/13: Ipswich MA. This is a tightly sealed home. My problem in designing it was I didn’t know the power of having all windows on the south-which is true south. Also, since my priority was having the view clear, I chose high visible transmittance which came with high SHGC.
Thanks for info re:roof insulation.
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Replies
Rita,
First of all, if your house is overheating during the summer, replacing your roofing is not the first remedy that comes to mind. A better remedy would be to increase the amount of insulation in your ceiling or roof.
However, if you need to replace your roofing for other reasons, there is no reason you can't choose metal roofing if you like metal roofing.
A cool roof should have both high solar reflectance (ability to reflect sunlight, measured on a scale of 0 to 1) and high thermal emittance (ability to emit thermal radiation, also measured on a scale of 0 to 1). More information here: http://coolcolors.lbl.gov/assets/docs/fact-sheets/Cool-roof-Q%2BA.pdf
If you want to use Energy Star criteria for evaluating your roofing options, you can. Here is a link to the Energy Star page on roofing products:
http://www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup&pgw_code=RO
If overheating is a problem... replacing the roof cladding does not sound like "top priority" to me either.
... in addition to increasing Insulation...Air sealing should be TOP Priority for ALL seasons.
Also consider that a "cool roof" (and "radiant barriers") may work against you during the Heating Season.
Which Ipswich? SD? MA? UK? Australia?
In heating dominated climates going with CRRC-rated cool roof finishes will increase annual energy use, but it's not a huge increase. But it also decreases the average temp of the roof deck, particularly the north side, which increases the likelihood of mold issues getting started.
There are many high-SRI metal roofing finishes to choose from (use the CRRC search function for the appropriate materials to be able to compare apples-to-apples), but there are no Ipswich's I know of in N. America where cool roof's make any sense.
If you DO re-roof, putting the appropriate amount of exterior foam on the roof deck (that would be R20 min, for MA: http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_8_par100.htm ) for dew point control and completing the insulation to code-R from the interior would take any roof-gains down to the "don't care" levels. In a code-min air-tight house window-gains dominate the cooling loads, which can be managed with awnings (on the south side) or exterior shades (particularly on the west side) if needed.